1. Field of the Invention
The invention relates to a control system and method for controlling an internal combustion engine, and more particularly to an engine control system and method for controlling a plurality of variable valve actuating mechanisms provided for a plurality of banks of the engine to change the operating characteristics of intake or exhaust valves.
2. Description of Related Art
A control system, which is related to the invention, for an internal combustion engine equipped with a variable valve actuating mechanism is described in, for example, Japanese Patent Application Publication No. 2003-41977. The variable valve actuating mechanism has an actuator that changes the duration of each intake valve, which corresponds to the period during which the intake valve is open. The control system described in the above-identified publication learns the position of the maximum-lift end of the actuator (which provides the longest duration of the intake valve) and the minimum-lift end (which provides the shortest duration), so as to control the variable valve actuating mechanism with high accuracy.
When conditions that allow the operation of the variable valve actuating mechanism are satisfied for the first time after an ignition switch is turned on, for example, the control system as described above learns the position of the maximum-lift end of the actuator corresponding to the longest duration and the position of the minimum-lift end corresponding to the shortest duration. The control system then operates the engine while varying the duration with reference to the thus learned positions.
Occasionally, the learned values of the positions of the maximum-lift end and the minimum-lift end may be cleared or eliminated due to, for example, electrical noise. In this case, the operating position (absolute position) of the variable valve actuating mechanism cannot be detected until the reference positions are learned again. In the case of a V-type engine having two banks, for example, a learned value or values associated with the variable valve actuating mechanism for only one of the two banks may be eliminated. However, the issue of how to re-learn the reference positions without affecting the operation of the running vehicle or engine remains.